1. Field of the Invention
The present invention relates to a display device, and more particularly to a technique which is effectively applicable to a method for detecting a defect of a display device which includes photo sensor elements within a display panel.
2. Description of Related Art
A TFT-type liquid crystal display module which uses a thin film transistor as an active element can display images of high definition and hence, the TFT-type liquid crystal display module has been used as a display device such as a display for a television receiver set or a personal computer. Particularly, a miniaturized TFT-type liquid crystal display device has been popularly used as a display part of a mobile phone.
In general, with respect to the liquid crystal display module, in a region surrounded by two neighboring scanning lines (also referred to as gate lines) and two neighboring video lines (also referred to as source lines or drain lines), a thin film transistor which is turned on in response to a scanning signal from the scanning line and a pixel electrode to which a video signal from the video line is supplied via the thin film transistor are formed thus forming a so-called pixel.
A region which forms a plurality of pixels therein constitutes a display region, and a peripheral region exists surrounding the display region. Semiconductor chips which constitute a video drive circuit and a scanning line drive circuit or lines which respectively connect the scanning lines and the video lines in the display region are arranged in the peripheral region.
In this manner, with respect to the liquid crystal display module for the mobile phone, in the peripheral region, the semiconductor chips which constitute the video drive circuit and the scanning line drive circuit or the lines which respectively connect the scanning lines and the video lines in the display region are arranged. Recently, along with the increase of the image display region, the peripheral region is narrowed.
Accordingly, there has been a drawback that it is impossible to ensure a space for forming an inspection terminal for inspecting by turning on the liquid crystal display panel in a peripheral region.
Here, without forming the inspection terminal, it may be possible to use a connection terminal between the scanning line and the semiconductor chip or a connection terminal between the video line and the semiconductor chip as the inspection terminal. In this case, however, there exists a drawback that the alignment between a terminal of an inspection device and the connection terminal becomes difficult.
Accordingly, as a method for detecting a defect of the liquid crystal display panel, a pseudo dynamic lighting inspection (hereinafter referred to as QD lighting inspection) is adopted (see following patent document 1, patent document 2).
According to the QD lighting inspection, the number of inspection terminals can be reduced and hence, even when the peripheral region becomes narrow, it is possible to arrange the inspection terminal for performing the inspection by turning on the liquid crystal display panel.
On the other hand, with respect to the liquid crystal display module for a mobile phone, there has been known a liquid crystal display module which includes a photo sensor element in the inside of a liquid crystal display panel.
This liquid crystal display module which includes a photo sensor element in the inside of a liquid crystal display panel can control brightness of a white light emitting diode which constitutes a backlight in response to an output (in other words, brightness of external light) of the photo sensor element.
In the liquid crystal display module which includes the photo sensor element in the inside of the liquid crystal display panel, as a general technique for inspecting the photo sensor element and first to third photo sensor lines which are connected to the photo sensor element, it may be possible to consider a current monitoring system which determines open short-circuiting by monitoring a difference current value by applying a signal to respective input terminals of the first to third photo sensor lines.
As prior art literatures related to the present invention, followings are named.
Patent document 1: JP-A-2004-101863
Patent document 2: JP-A-2001-324721